Visbreaking is a mild cracking operation used to reduce the viscosity of heavy residua. The heavy residua are sometimes blended with valuable light oil, or cutter stocks, to produce fuel oils of acceptable viscosity. By use of visbreakers, the viscosity of the heavy residua is reduced so as to lower the requirement of the cutter stock. The ultimate objective of the visbreaking operation is to eliminate completely the need for cutter stocks.
Sometimes visbreakers are also used to generate more gas oils for catalytic cracking and naphtha for reforming to increase the gasoline yield in the overall refining operation. To achieve these goals, the visbreaker has to be operated at high enough Severity to generate sufficient quantities of lighter products.
The visbreaker feedstock usually consists of a mixture of two or more refinery streams derived from sources such as atmospheric residuum, vacuum residuum, furfural-extract, propane-deasphalted tar and catalytic cracker bottoms.
The economic and environmental factors relating to upgrading of petroleum residual oils and other heavy hydrocarbon feedstocks have encouraged efforts to provide improved processing technology, as exemplified by the disclosures of various U.S. patents which include U.S. Pat. Nos. 2,160,814; 2,358,573; 2,695,264; 2,733,192; 3,065,165; 3,696,027; 3,730,879; 3,775,303; 3,870,621; 3,876,530; 3,882,049; 3,897,329; 3,905,893; 3,901,792; 3,964,995; 3,985,643; 4,016,067; 4,054,504; 4,379,747; and the like.
Accordingly, it is an object of this invention to provide a process for improving the performance of visbreakers for the production of an increased yield of light products such as heating oil and gas oil from a heavy oil feedstock.
It is another object of this invention to provide a process for the production of a visbroken hydrocarbon product which meets heating oil viscosity specifications with little or no blending with external cutter stocks, and which has a metals content less than about 50 parts per million.
It is a further object of this invention to provide an improved visbreaking process for the production of a visbroken effluent which is stable and compatible and which can be blended with other fuel range stocks without formation of sludge or precipitate.
Other objects and advantages of the present invention will become apparent from the accompanying description and illustrated data.